Invasive rodent eradication on islands

  • Published source details Howald G., Donlan C.J., Galván J.P., Russell J.C., Parkes J., Samaniego A., Wang Y., Veitch D., Genovesi P., Pascal M., Saunders A. & Tershy B. (2007) Invasive rodent eradication on islands. Conservation Biology, 21, 1258-1268.


Introduced mammals are one of the greatest threats to oceanic island biodiversity and a great number of extinctions and associated ecosystem change has been attributed to invasive rodents, especially rats Rattus spp. Techniques for eradicating rodents from islands were initially mostly developed over 20 years ago since when methods have significantly developed. A literature review on invasive rodent eradications was undertaken to assess its current state and identify actions to make it more effective.

Data from published and grey literature, and personal communications on rodent eradications were compiled. As rodents are difficult to detect at low densities, a widely accepted indicator of eradication success is no detection after 2 years of intensive monitoring following the eradication effort. This was therefore used as the measure fgor success in the review. Secondary eradication efforts of small rodent populations that reinvaded islands following a previous, successful eradication campaign were not included. This may be a common occurrence on islets/islands located close to a 'mainland' source population.

The review identified worldwide, 332 successful rodent eradications, 35 failed and 20 campaigns of unknown result as having been undertaken. Invasive rodents have been eradicated from 284 islands (totaling 47,628 ha in area). With the exception of two small islands, rodenticides were used in all eradication campaigns. The rodenticide brodifacoum was used in 71% of cases over 91% of the total area treated. The most frequent rodenticide distribution methods (from most to least) are bait stations, hand broadcasting, and aerial broadcasting. However, campaigns using aerial broadcast covered 76% of the total area treated.

Mortality of native vertebrates due to non-target poisoning was sometimes reported but affected species quickly recovered to pre-eradication population levels or higher. A variety of methods have been developed to mitigate non-target impacts, and further refinements may be expected to further minimize impacts.

In light of evidence from the review, the authors recommend that managers should routinely remove invasive rodents from islands <100 ha that lack vertebrates susceptible to non-target poisoning. For larger islands and those that require non-target mitigation, expert consultation and greater planning are needed.

With the exception of house mice Mus musculus, island size may no longer be the limiting factor for successful rodent eradications; social acceptance and funding may become more important. To be successful in the long-term, it may be necessary to integrate large-scale eradication campaigns with programs to improve the livelihoods of human residents, island biosecurity and reinvasion responses.

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